The invention relates to addressable downhole activation systems.
To complete a well, one or more sets of perforations may be created downhole using perforating guns. Such perforations allow fluid from producing zones to flow into the wellbore for production to the surface. To create perforations in multiple reservoirs or in multiple sections of a reservoir, multi-gun strings are typically used. A multi-gun string may be lowered to a first position to fire a first gun or bank of guns, then moved to a second position to fire a second gun or bank of guns, and so forth.
Selectable switches are used to control the firing sequence of the guns in the string. Simple devices include dual diode switches for two-gun systems and concussion actuated mechanical switches or contacts for multi-gun systems. A concussion actuated mechanical switch is activated by the force from a detonation. Guns are sequentially armed starting from the lowest gun using the force of the detonation to set a switch to complete the circuit to the gun above and to break connection to the gun below. The switches are used to step through the guns or charges from the bottom up to select which gun or charge to fire. However, if a switch in the string is defective, then the remaining guns above the defective gun become unusable. In the worst case situation, a defective switch at the bottom of the multi-string gun would render the entire string unusable.
Other conventional perforating systems do not allow for the confirmation of the identity of which gun in the string has been selected. The identity of the selected gun is inferred from the number of cycles in the counting process. As a result, it is possible to fire the wrong gun unless precautions are followed, including a taking physical measurement, such as a voltage drop or amount of current to determine which gun has been selected before firing. This, however, adds complexity to the firing sequence. Furthermore, such precautionary measures are typically not reliable.